Tubular water quench process with water film cooling

ABSTRACT

Film of an organic thermoplastic polymer is manufactured by drawing an extruded, inflated, hot, tubular film from an extruder and passing the film into contact with layers of cooling liquid supported by symmetrically disposed collapsing elements adapted to effect a partial but not complete collapse of the tubular film to the lay flat form, cooling liquid being simultaneously supplied to a plurality of locations distributed over the surfaces of the collapsing elements at a rate sufficient to maintain layers of cooling liquid thereon.

United States Patent van Kralingen [4 1 Oct. 24, 1972 [54] TUBULAR WATERQUENCH PROCESS WITH WATER FILM COOLING [72] lnventor: Peter H. vanKralingen, Delft,

Netherlands [73] Assignee: Shell Oil Company, New York, NY.

[22] Filed: Aug. 13, 1969 [21] Appl. No.: 849,849

[30] Foreign Application Priority Data Dec.31,1968 GreatBritain..61,899/68 52] U.S.Cl. ..264/95, 264/178 264/237, 264/348, 425/71,425/326 511 int. Cl ..B29c 17/07, 1329c 25/00, B29d 7/20 [58] Field ofSearch ..264/95, 175, 237, 178, 348; 18/14 A, 14 S, 8 QA; 425/325, 326,71

[56] References Cited UNITED STATES PATENTS 1,591,170 7/ 1926 Lutyens..264/175 2,337,927 12/ 1943 Reichel et al. ..264/95 UX 3,274,317 9/ 1966 Batosti et al ..264/95 3,377,413 4/ 1968 Jansson et al ..264/953,543,334 12/1970 Sudo ..264/95 FOREIGN PATENTS OR APPLICATIONS1,093,018 1 H1967 Great Britain ..264/95 Primary Examiner-Robert F.White Assistant ExaminerJeffery R. Thurlow Attorney-Joseph W. BrownABSTRACT Film of an organic thermoplastic polymer is manufactured bydrawing an extruded, inflated, hot, tubular film from an extruder andpassing the film into contact with layers of cooling liquid supported bysymmetrically disposed collapsing elements adapted to effect a partialbut not complete collapse of the tubular film to the lay flat form,cooling liquid being simultaneously supplied to a plurality of locationsdistributed over the surfaces of the collapsing elements at a ratesufficient to maintain layers of cooling liquid thereon.

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INVENTOR:

PETER H. VAN IKRALINGEN 2mm HIS ATTORNEY PATENTED 24 I97? 8 7 0O 763 sum2 OF 2 FIG 5 FIG. 6

FIG. 7 FIG. 8

INVENTORI PETER H. VAN KRALINGEN HIS ATTORNEY TUBULAR WATER QUENCHPROCESS WITH WATER FILM COOLING The present invention is concerned withthe manufacture of films from organic thermoplastic polymers, forexample, polypropylene by 'a process (hereinafter referred to as aprocess of the kind defined) in which an internally-blown film isextruded continuously and in a downward direction from an organicthermoplastic polymer melt and the resulting blown tube or bubble iscooled and flattened to lay-flat form. The present invention is alsoconcerned with the resulting films in layflat form or slit into sheets,tapes, ribbons or filaments.

It is known to employ water as a cooling medium in processes of the kinddefined above. Many proposals have been made in regard to the manner inwhich the blown tube is brought into contact with the cooling water. Forexample, the use of a water bath has been proposed. However, the processof this proposal is difficult to control and produces a poor clarityproduct unless special techniques such as described in US. Pat.Application Ser. No. 710,566, Chein-Ho, (now US. Pat. No. 3,539,669),are employed. Another method based on the concept of a water cascade onthe outer surface of the blown tube has also been proposed. But thismethod also has disadvantages such as film size limitations. There isalso a tendency for variations in the film cooling efficiency occurringwith small changes in the film tube diameter. The cascade can be formedby passing the blown tube through a fixed guide means such as a ring ortube provided, for example, with an annular water trough. The wateroverflowing from the trough passes down the outer surface of the blowntube as an enveloping curtain or cascading column, The curtain or columncan be wholly or mainly exposed to the surrounding atmosphere as in thecase of the method described, for example, in UK. Pat. Nos. 876,460 and872,1 in which the cooling water is supplied by one or more annularrings through which the blown tube passes. Alternatively, the curtain orcascading column of water can be confined within the annular spaceformed between the outer surface of the blown tube and the inner surfaceof a-cylindrical metal tube through which the blown tube passes as inthe case of the method described, for example, in U.K. Pat. Nos. 853,745and 741,963. The cooling water can also be supplied by sprayssurrounding the top of the blown tube in place of the aforesaid annulartrough. In another approach to the problem of effecting adequate coolingof the blown tube, the latter is passed through a water bath while itsinterior surface is colled by contact with an internal, smooth-surfacedcooling mandrel. Such a technique is described, for example, in UK. Pat.Nos. 1,061,342 and 1,043,933. The concept of cooling the interior of theblown tube with a water curtain or cascade has also been proposed butinevitably this leads to complications in both the design of theequipment and in the operation thereof.

In general, water cooling techniques involving the use of an annularring or tube through which the internally-blown tube must pass sufferthe disadvantage of lack of flexibility in regard to the size of theblown tube which can be handled. To be effective the ring or tube mustprovide an even water cascade or curtain over the whole of the outersurface of the blown tube. In practice this usually means that aparticular equipment can produce only one size of blown tube. Moreoverlittle or no variation in blown tube diameter can be tolerated duringthe operation of the equipment.

Other important factors arise in the operation of any equipment in whichcooling is effected by means of a water curtain or cascade on theexternal and/or internal surface(s) of blown tube. For example, an evencooling over the whole surface of the blown tube is essential not onlyin order to maintain stability of the blown tube but also to avoidoptical variations in the resulting thermoplastic film. Also, when thecooling water is applied to the blown tube by means of sprays whichexert pressure on the external surface thereof particular care must betaken to avoid localizedconcavities or convexities which can arise fromlocal variations in the water pressure over the tube surface. With anyof the methods hitherto proposed for supplying the cooling water to theblown tube the maintenance of an enveloping cascade or curtain ofcooling water of the same water thickness round the whole circumferenceof the blown tube can be difficult. This is particularly so when theblown tube passes through a surrounding metal tube of significant depthwithin which local hot spots can easily develop due to localizedthinning of the water film.

The present invention is based on a new approach to the cooling problemin which the blown tube is pressed against supported water films solelyby the fluid pressure within the blown tube. The blown tube is therebyboth cooled and partially flattened under conditions which result ineven cooling and even pressure over the entire water-cooled surface. Thewater films are supported in such a manner that within relatively widelimits blown tubes of any diameter can be handled. Minor variations inthe diameter of the blown tube which occur from time to time duringoperation of the process have substantially no effect on the opticalproperties of the resulting film or on the stability of the blown tubeitself or on the cooling efficiency of the process.

According to the present invention a process of the kind defined for themanufacture of film from a thermoplastic organic polymer, comprisesdrawing an extruded, inflated, hot, tubular film from an extruder andpassing the hot tubular film into contact with layers of cooling liquidsupported by symmetrically disposed collapsing elements adapted toeffect a partial but not complete collapse of the tube to the lay-flatform, cooling liquid being supplied simultaneously to a plurality oflocations distributed over the surfaces of the collapsing elementsthrough a plurality of apertures or channels in the walls of thecollapsing elements at a rate sufficient to maintain the layers ofcooling liquid thereon. The present invention also includes theresulting film.

The present invention also includes apparatus for cooling an extruded,inflated, hot, tubular film of an organic thermoplastic polymer duringthe manufacture of film by a process of the kind defined. The apparatuscomprises a pair of collapsing elements adapted to effect a partial butnot complete collapse of a hot inflated film to the lay-flat form, eachof collapsing elements being provided with means for supplying a coolingliquid simultaneously to a plurality of locations distributed over thesurface thereof through a plurality of apertures or channels in the wallof the collapsing element in such a manner that a layer of coolingliquid can be maintained on the surface.

' Although not limited in regard to the shape and nature of collapsingelements used, the process of the present invention will usually employtwo such elements. The general shape and symmetrical disposition withrespect to the blown, tube of such collapsing elements can be generallysimilar to the collapsing boards or frames well known in the filmmanufacturing and processing art, but other forms of collapsing elementscan be used. Usually the cooling liquid will be water. Preferably thecollapsing elements are used in combination elements. The partiallycollapsed blown tube is led into the bath and between nip rollersdisposed therein which effect a complete collapse of the blown tube tothe lay-flat form. Preferably the collapsing elements are disposed so asto provide guiding surfaces which support the partially collapsed blowntube as it enters the cooling liquid bath in order to prevent wrinklingor marking thereof.

Advantageously the collapsing elements are made from porous metal, thepores constituting a multiplicity of apertures in the walls thereof. Insuch cases porous metal plates of any suitable shape can be employed.

Cooling liquid can be supplied thereto by providing a water chamber (oreven a plurality of separate inlet ports) at the rear of the plates. Thechamber extends over part or all of the rear surface thereof.Altematively, plates having a plurality of channels or grooves in thesurface thereof or having a number of spaced apertures of anyconventional shape, opening into said surface, for example, circularholes can be used in place of porous metal plates. The collapsingelements can be flat plates or plates shaped in the direction of filmtravel so as to provide support for the curved lower part of the blowntube. The elements can also be at right angles so as to correspond tothe shape of the lower part of the blown tube at its line of firstcontact with the collapsing elements. Porous or apertured rollers canalso be used as collapsing elements. Alternatively, each collapsingelement can comprise a box-like structure having a plurality of freelyrotatable rollers disposed in longitudinal slots in one surface thereofso as to project slightly therefrom. The rollers rotate with clearancein the slots so as to permit cooling liquid to flow from the hollowinterior of the collapsing element onto the surfaces of the rollers andonto those portions of the surface of the collapsing element which liebetween the rollers. If desired, the collapsing elements may be joinedby side portions where the elements come close together at their loweredges to effect cooling of the two opposed side portions of the blowntube which otherwise might not contact the collapsing elements.

The process of the present invention provides for an even water coolingof a downwardly-extruded blown film by means of water layers in whichthe water flow is parallel to the direction of movement of the film. Atthe same time a partial flattening of the blown tube is achieved bymeans of symmetrically disposed collapsing elements. Usually thispartial collapse of the blown tube will be such that the tube is broughtquite near to the lay-flat form. Preferably the line of first contactbetween the blown tube and each of the collapsing elements approximatesa horizontal line over as much as possible of the tubes length. This maybe achieved by suitably shaping the tube-contacting surface of each ofthe collapsing elements in the manner described herein.

The present invention can be applied to the manufacture of film from anythermoplastic organic polymer which is suitable, in regard to softeningpoint and melt stability, for use in a process of the kind defined.Suitable thermoplastic organic polymers include, for example, polyvinylchloride, polyesters, nylons and polyolefins. The present invention isparticularly applicable to crystalline polymers, for example the nylonsand polyolefins. The term polyolefin is used herein to include an olefinpolymer or copolymer as such and also a polymer composition the majorpart of which is a polyolefin or mixture thereof. Examples ofpolyolefins which can be used in carrying out the process of the presentinvention are polyethylene and polypropylene. The present process isparticularly suitable for the manufacture of high clarity polypropylenefilm having good physical properties.

It is a particular advantage of the invention that various widths andthicknesses of film can be manufactured at high throughput rates withthe same cooling unit, and in general blow-up ratios in the range of 0.1to 2.0 can be employed.

The present invention will be further described with reference to theaccompanying diagrammatic drawings in which: g FIG. 1 is a schematicdrawing showing a general arrangement for film manufacture in accordancewith the present invention,

FIGS. 2-8 are schematic representations showing various forms ofplate-like collapsing elements,

FIG. 9 is a schematic drawing showing an alternative form of collapsingelement, and

FIG. 10 is a schematic representation showing the use of collapsingelements in the form of porous rollers.

Referring to FIG. 1, a hot blown tube 11 of, for example, polypropylene,is extruded downwardly from an extruder die 12 of conventional form andis cooled, in accordance with the present invention, by means of acooling unit comprising a pair of porous plates 13, 14 which constitutethe collapsing elements and a body of cooling water contained in a tank15. The plates 13, 14 also effect a partial collapse of the blown tube11,

complete collapse to the lay-flat form being achieved by driven nippingrollers l6, 17 located within the cooling water in the tank 15. Thesenipping rollers 16, 17 also serve to draw down the blown tube 1 1 fromthe extruder die 12. The lay-flat film is removed over a roller 18 byconventional haul-off equipment (not shown). Each of the porous plates13, 14 comprises a thin hollow box having a porous front surface 13a,14a adapted to contact the blown film, and an inlet pipe 19, 20 forsupplying water under pressure to the interior of the box. In'operationthe water in the interior of the box permeates to the front surface 13aor 14a through the pores thereof to form a layer of cooling liquid onthe surface 13a or 14a. The size of the pores is such that under thewater pressure employed an adequate thin layer of cooling water ismaintained on the surfaces 13a and 14a during operation of the coolingunit. The cooling water can be supplied to the collapsing elements atambient temperature, for example at 10 to 20C, and its rate of supplyshould be such that thin layers of water are maintained over the wholesurface thereof during operation of the process.

Referring to FIGS. 28, FIG. 2 shows a collapsing element in the form ofa plate 21 having a large plurality of convex protuberances 22, all ofthe same size and shape, on its surface. The spaces between theprotuberances 22 provide channels for the supply of cooling liquid tothe whole surface of the plate 21, the liquid being supplied from thetop of the plate. FIG. 3 shows a collapsing element in the form of ahollow box 23 having an apertured front surface containing a number ofdiamond-shaped apertures through which cooling water can be supplied.FIG. 4 shows a somewhat similar collapsing element in which theapertures comprise slits 24. FIGS. 5 and 6 show porous plate collapsingelements which are shaped in the direction of travel of the blown tubeto provide additional guidance and support for the blown tube. FIG. 7shows a porous plate collapsing element which is shaped at right anglesto the direction of travel of the blown tube in order to straighten theline of first contact of the blown tube with the collapsing elements. Aswill be apparent from FIG. 1 this line of first contact (shown dotted atA) tends to be parabolic in form when the plates have a flat surface.

The present invention can be illustrated by the following exampleEXAMPLE Polypropylene film was manufactured in accordance with theprocess described with reference to FIG. 1 of the accompanying drawings,the collapsing elements comprising porous plates each shaped to providea downwardly and inwardly extending flat surface 40 centimeters inlength for partially collapsing, and cooling, the blown tube and a fiatvertical portion forming a guide for the film as it entered the waterbath. The bottom edge of this vertical portion was therefore below thewater surface, and the two plates were disposed so that their respectivevertical portions were 2 millimeters apart. The collapsing portion ofeach of the collapsing elements was at an angle of 160 to the verticaland the mid-part of each collapsing element lying between the collapsingportion and the vertical portion was curved, the radius of curvaturebeing 12.5 centimeters. The water level in the tank was just below thisradiused mid-part of the collapsing elements. The collapsing elementscomprised sheets of porous copper material. Cooling water was suppliedthereto by water chambers welded to the back of the plates and coveringthe upper part of the rear surfaces thereof. The polypropylene wasextruded downwardly in conventional manner. In a number of runs theblow-up ratio was varied to produce films of various widths, with filmthicknesses of 30, 50 and 100 microns. Using a 200 millimeter diameterannular extrusion die and operating at a melt temperature of 240C,polypropylene films of good optical and mechanical properties wereobtained under the following conditions 15C 5 liters per minute Coolingwater input temperature Cooling water supply rate (to both collapsingelements) Blow-up ratios Film production speed 0.4; 0.6; 0.8; L2 l5,30meters/minute ganic thermoplastic polymer at a rate of production of15-30 meters/minute which comprises 1. drawing an extruded, inflated,hot, tubular film 7 from an extruder; while at the same time 2.supplying a cooling liquid simultaneously to a plurality of locationsdistributed over the surfaces of symetrically disposed plate-likecollapsing elements, which are adapted to effect partial but notcomplete collapse of the tubular film to the lay fiat form, said coolingliquid being supplied at a rate sufiicient to maintain layers of coolingliquid on said collapsing elements; and

3. passing said hot, tubular film into initial liquid quenching contactwith the saidlayers of cooling liquid wherein said contact is providedsolely by the pressure within the tubular film.

2. A process as claimed in claim 1, wherein said cooling liquid iswater.

3. A process as claimed in claim 1, wherein said partially collapsedfilm is passed into a cooling liquid bath and therein is completelycollapsed to lay-flat form.

4. A process as claimed in claim 1, wherein said hot tubular film ispassed into first contact with said layers of cooling liquid said firstcontact approximating a horizontal line.

2. supplying a cooling liquid simultaneously to a plurality of locationsdistributed over the surfaces of symetrically disposed plate-likecollapsing elements, which are adapted to effect partial but notcomplete collapse of the tubular film to the lay flat form, said coolingliquid being supplied at a rate sufficient to maintain layers of coolingliquid on said collapsing elements; and
 2. A process as claimed in claim1, wherein said cooling liquid is water.
 3. A process as claimed inclaim 1, wherein said partially collapsed film is passed into a coolingliquid bath and therein is completely collapsed to lay-flat form. 3.passing said hot, tubular film into initial liquid quenching contactwith the said layers of cooling liquid wherein said contact is providedsolely by the pressure within the tubular film.
 4. A process as claimedin claim 1, wherein said hot tubular film is passed into first contactwith said layers of cooling liquid said first contact approximating ahorizontal line.